Investigation of the Role of Polyploidization in Glial Cells During the Development of the Drosophila Nervous System

Investigation of the Role of Polyploidization in Glial Cells During the Development of the Drosophila Nervous System
Author: Laura Elizabeth Frawley
Publisher:
Total Pages: 181
Release: 2018
Genre:
ISBN:
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Organogenesis is a complex process encompassing cell determination, cell differentiation, cell proliferation, and cell size regulation. The proper orchestration of these events ensures that each organ is scaled correctly and can function properly. Polyploidization is a process by which cells increase their DNA content and is used across species to generate large cells. Our lab had previously determined that subperineurial glia (SPG) of the Drosophila melanogaster nervous system become polyploid by both the endocycle and endomitosis. These are two cell cycle variants employed to produce polyploid cells that differ in the latter undergoing some aspects of mitosis but not cytokinesis. Polyploidization of the SPG is critical for blood-brain barrier (BBB) function. Here, we determined that the developmental switch from endocycling to endomitotic SPG occurs in about 70% of SPG in the brain lobes by the second larval instar. The SPG in the ventral nerve cord and peripheral nervous system solely endocycle. We demonstrated that both the Notch signaling pathway and the String Cdc25 phosphatase are critical in determining whether SPG endocycle or endomitose. Experiments manipulating the percentage of cells that are endocycling versus endomitotic highlight key differences between endocycling and endomitotic SPG. We find that endomitotic SPG cells are capable of achieving higher ploidy and cell area values than endocycling cells and are essential to the integrity of the BBB. Strikingly, we find that endocycling SPG within the ventral nerve cord retain the ability to undergo endomitosis when the Notch signaling pathway or the String Cdc25 phosphatase are altered. Further, we showed that a second glial cell type in the peripheral nervous system, wrapping glia (WG), is polyploid and determined that total WG ploidy correlates with nerve length. Interestingly, when WG ploidy was reduced, we found that axonal ensheathment is defective. We also established that the three WG per peripheral nerve differentially contribute to overall ploidy. Axonal ensheathment throughout the entire nerve seems to be dependent on position along the anterior-posterior larval body axis. Finally, we find that reduction of DNA replication components causes reduced WG ploidy only in longer peripheral nerves.

Endocytic Regulation of Notch Signaling in Drosophila Melanogaster Neural Progenitor Cells

Endocytic Regulation of Notch Signaling in Drosophila Melanogaster Neural Progenitor Cells
Author: Seth Andrew Johnson
Publisher:
Total Pages: 264
Release: 2016
Genre:
ISBN:
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Notch signaling is a ubiquitously used signaling pathway that is highly conserved and used throughout metazoan development. Understanding the regulation of Notch signaling is becoming increasingly important in determining the mechanism and treatment for the myriad of human Notch-related diseases. In Drosophila. melanogaster, the development of external sensory organs provides a context in which Notch can be manipulated and phenotypes can be easily interpreted. Here, we expand upon the growing field of Notch regulation through endocytic trafficking by examining the role of Numb and Sara endosomes. Numb is a potent Notch inhibitor whose function is conserved in higher organisms, but whose mechanism of action has remained elusive. In this study, we dispel a previous hypothesis that Numb promotes Notch internalization and instead demonstrate that Numb is a suppressor of Notch endocytic recycling. In support of this, we show that Numb is necessary and sufficient for Notch trafficking to late endosomes/lysosomes to promote degradation. We do this by employing a novel technique that is able to distinguish recycled Notch from other populations within the cell. In addition, we show that the cell fate determinant Lethal (2) Giant Larvae, can also suppress Notch recycling, but at a step upstream of Numb. Results from this study help to answer a long-standing questions in the field of Notch signaling, by demonstrating the role of Numb in Drosophila. We also extended our investigation of endocytic Notch regulation by determining the role of a sub-population of early endosomes positive for Sara. We show that these Sara endosomes are trafficked preferentially to Notch activated cells, but do not contain appreciable levels of Notch. While we conclude that the Sara endosomes do not seem relevant to Notch signaling, we show that the mechanism of Sara endosome trafficking is likely tied to global anterior-posterior cues and not related to cell fate determinants. Results from our studies have important implications in the designing of treatments for Notch related dysfunctions that depend on an exquisite understanding of Notch regulation.

Molecular Mechanisms of Notch Signaling

Molecular Mechanisms of Notch Signaling
Author: Tilman Borggrefe
Publisher: Springer
Total Pages: 417
Release: 2018-07-20
Genre: Science
ISBN: 3319895125
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This book describes the Notch signaling pathway with a focus on molecular mechanisms. The Notch signaling pathway is a seemingly simple pathway that does not involve any second messenger. Upon ligand binding two consecutive proteolytic cleavages of the NOTCH receptor release the Notch intracellular domain from the membrane. The Notch intracellular domain migrates into the nucleus and activates gene expression. Recently, new technologies allowed us to better understand this pivotal signaling cascade and revealed new regulatory mechanisms. The different chapters cover many aspects of the Notch signaling focusing on the mechanisms governing the receptor/ligand interaction as well as on the downstream intracellular signaling events. Aspects of both canonical and non-canonical signaling are discussed and the function of Notch signaling in physiological and pathological contexts are elucidated. This book is not only intended for experts but it should also be a useful resource for young, sprouting scientists or interested scientists from other research areas, who may use this book as a stimulating starting point for further discoveries and developments.

Drosophila T-box Transcription Factor Midline Functions in the Notch-Delta Signaling Pathway to Regulate Sensory Organ Precursor Cell Fate and Cell Survival and Embryonic Development Profile of Midline, Senseless, and Achaete in the CNS and PNS

Drosophila T-box Transcription Factor Midline Functions in the Notch-Delta Signaling Pathway to Regulate Sensory Organ Precursor Cell Fate and Cell Survival and Embryonic Development Profile of Midline, Senseless, and Achaete in the CNS and PNS
Author: Joseph Dean Saucier
Publisher:
Total Pages: 54
Release: 2013
Genre: Central nervous system
ISBN:
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The gene mid of Drosophila is a highly conserved gene that codes for a T-box transcription factor with similar functionality to its vertebrate homolog Tbx20. Mid and Tbx20 are important for their roles in heart and CNS development. Additionally, these transcription factors aid in proper eye development but this area of research is vastly understudied. This study uses the eye of Drosophila to report that mid and its paralog H15 expression aid in the specification of sensory organ precursor (SOP) cell fates and cell survival in the pupal eye imaginal disc. Using RNAi interference to reduce mid expression resulted in the loss of interommatidial bristles as well as cell death due to the misspecification of SOP cells during pupal development. We completed genetic studies to place mid in the Notch-Delta genetic pathway because it is known to specify SOP cell fates and were able to determine that Mid functions downstream of Notch, upstream of the Enhancer of Split (E(Spl)) gene complex, and tentatively parallel with Suppressor of Hairless (Su(H)) in the pathway. Additionally, mid interactions with extramacrochaete (emc) and Senseless (sens) play a role in cell survival. These studies suggest that Mid functions within the Notch- Delta signaling pathway with a dual role of cell-fate specification and cell survival. Another aspect of this research study was to evaluate the role of Mid in the developing central nervous system (CNS) and peripheral nervous system (PNS) of Drosophila embryos. Mid expression was compared to the expression of Sens and Achaete (Ac), SOP cell markers during various stages of embryonic development. Our results show a coordinated co-expression pattern of Sens and Ac with Mid. Sens is highly expressed in the PNS of stages prior to stage 12 and then fades. Ac is expressed in the neurons of the CNS and PNS in early stages and continues after stage 12, which is when Mid expression begins. Ac is co-expressed with Mid beginning in stage 12. Further experiments will be performed using mid-RNAi embryos to evaluate if reducing mid expression affects the expression patterns of Sens and Ac. This research has clinical applications to further the understanding of developmental and neurodegenerative diseases of the CNS, PNS, and eye. Additionally, Mid may have a link to the development of cancer, an area of research that will be studied in the Leal lab in the future.--P. vi-vii.